Since the 1800's biometric information has been collected from human fingers and hands by means of ink and paper. For the purposes of this document, the term fingerprint is used to mean the skin surface friction ridge detail of a single fingerprint, partial fingerprint or any portion of the skin surface friction ridge of up to and including the entire hand or foot. In recent years various electronic fingerprint scanning systems have been developed utilizing optical, capacitance, electric field, direct pressure, thermal, and acoustic methods. Methods based upon acoustics, ultrasound, capacitance, and electric field measurement have proven to be the most accurate, because they are virtually immune to the effects of grease, dirt, paint, ink and other substances that may by present on the friction ridge skin.
For illustrating the invention, we will refer to the biometric object as a finger, but it should be understood that the invention is not limited to fingers. When the biometric object is a finger, the desired information may be the location of the ridges and valleys of the fingerprint. Such location information can be compared to a database of location information in order to determine whether the fingerprint matches fingerprint information stored in the database for identification purposes. Or, the location information may be used to create an image of the fingerprint.
Existing devices that utilize the electrical characteristics of a linger to produce information about a fingerprint include fingerprint scanners that sense capacitance or an electric field, including those that rely on dielectric material or electroluminescent material. Biometric scanners that use an electric field and/or capacitance sensors to obtain information about a biometric surface, such as a fingerprint, are referred to herein as EF/C Biometric Scanners. Existing EF/C Biometric Scanners are susceptible to damage caused by mechanical abrasion and electrostatic discharge (“ESD”).
EF/C Biometric Scanners may offer an advantage in that they may be able to provide improved imaging in cases where there may be poor acoustic impedance matching between the friction skin of the fingerprint and an ultrasound scanner's platen, such as may be encountered when the friction skin is very dry. Capacitance and electric field sensors are, however, prone to mechanical abuse and damage, and they are especially susceptible to damage from ESD.